arXiv subjects

E. Bauer

Publications and source records attributed to E. Bauer.

64 records · Page 4Linked to original sources

arXiv2004

Complex magnetic phase diagram of CePd_{2-x}Ni_xAl_3 around its critical concentration

Thermal, magnetic and transport measurements are reported on CePd_{2-x}Ni_xAl_3 in the 0<= x <= 1 range, including the effect of pressure (p) and magnetic field on some selected samples. The low temperature results indicate that long range antiferromagnetic order is stable up to x=0.2, while between 0.25 and 0.5 magnetic disorder gives rise to non-Fermi-liquid (NFL) behavior. In this region, the low temperature specific heat can be described by the sum of two components, the major one showing a C_P/T=gamma_0 -gamma_1 T^(1/2) dependence, while the minor one includes a decreasing number of degrees of freedom related to a residue of short range order. The latter extrapolates to zero between 0.45<x_{cr}<0.5. Electrical resistivity (rho) studies performed under pressure for x=0.5 allow to investigate the evolution of the NFL state right above the critical point, where the exponent of rho ~ T^n is found to increase from n=1 (for p=0) up to n=2 (for p=12 kbar). The latter is observed for x=1.0 already at normal pressure, indicating the onset of the Fermi Liquid behavior. Doping and pressure effects are compared by fitting high temperature resistivity data employing a unique function which allows to describe the evolution of the characteristic energy of this series through a large range of concentration and pressure.

cond-mat.str-el↗

arXiv2003

Heavy fermion superconductivity and magnetic order in non-centrosymmetric $CePt_3Si$

$\rm CePt_3Si$ is a novel heavy fermion superconductor, crystallising in the $\rm CePt_3B$ structure as a tetragonally distorted low symmetry variant of the $\rm AuCu_3$ structure type. $\rm CePt_3Si$ exhibits antiferromagnetic order at $T_N \approx 2.2$ K and enters into a heavy fermion superconducting state at $T_c \approx 0.75$ K. Large values of $H_{c2}' \approx -8.5$ T/K and $H_{c2}(0) \approx 5$ T refer to heavy quasiparticles forming Cooper pairs. Hitherto, $\rm CePt_3Si$ is the first heavy fermion superconductor without a center of symmetry.

cond-mat.str-el↗

arXiv2003

The role of the $Δ$(1232) on the longitudinal response in the inclusive electron scattering reaction

We have performed a many-body calculation of the longitudinal nuclear $(e,e')$ reaction employing a Second RPA (SRPA) formalism which contains the $Δ$(1232). More explicitly, our scheme contains RPA correlations as well as Hartree-Fock and second order self-energies, where an accurate evaluation of exchange terms is achieved. Using this formalism we have evaluated the longitudinal response function for $^{40}Ca$. We give final results at momentum transfers ranging from 300 up to 500 MeV/c, obtaining a good agreement with data.

nucl-th↗

arXiv2002

Nonmesonic Weak Decay of $Λ$ Hypernuclei within a Nuclear Matter Formalism

The nonmesonic weak decay of $Λ$ hypernuclei using nonrelativistic nuclear matter is studied. As the basic building block we use the Polarization Propagator Method developed by Oset and Salcedo. It is shown that the exact calculation of exchange terms is required. Using the Local Density Approximation we evaluate the nonmesonic decay width for $^{12}_ΛC$ and compare the result with a finite nucleus calculation, obtaining a qualitative agreement.

nucl-th↗

arXiv2002

An unusual interplay among disorder, Kondo-effect and spin-glass behavior in the Kondo lattices, Ce$_2$Au$_{1-x}$Co$_x$Si$_3$

We report the results of magnetic measurements for the solid solution Ce$_2$Au$_{1-x}$Co$_x$Si$_3$. The results reveal that this solid solution is characterized by a magnetic phase diagram (plot of magnetic transition temperature versus $x$) unusual for Kondo lattices. In particular, the spin-glass freezing induced by disorder is observed only for the compositions at the weak coupling limit; as one approaches the quantum critical point by a gradual replacement of Au by Co, this disorder effect is surprisingly suppressed in favor of long range antiferro-magnetic ordering in contrast to expectations. This unusual interplay between disorder, spin-glass freezing and the Kondo-effect calls for further refinement of theories on competition between magnetism and the Kondo effect.

cond-mat.str-el↗

arXiv2001

Thermal conductivity of superconducting MgB2

Thermal conductivity of superconducting MgB2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic - and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below Tc was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.

cond-mat.supr-con↗

arXiv2000

RPA quasi-elastic responses in infinite and finite nuclear systems

Quasi-elastic responses in nuclear matter and in $^{12}$C and $^{40}$Ca nuclei are calculated in ring approximation to investigate the finite size effects on the electromagnetic quasi-elastic responses. A method to simulate these effects in infinite systems calculations is proposed. The sensitivity of the results to the various terms of the residual interaction is studied. The results of nuclear matter RPA calculations are compared with those obtained in ring approximation to evidence the importance of the exchange terms.

nucl-th↗

arXiv2000

The Longitudinal and Transverse responses in inclusive electron scattering within the RPA framework

The longitudinal and transverse nuclear responses to inclusive electron scattering reactions are analyzed within the Random Phase Approximation (RPA) framework. Several residual interactions are considered and it is shown that the exchange terms in the RPA make very difficult to find an effective residual interaction capable of reproducing simultaneously the quasielastic peak of both the longitudinal and transverse responses. By means of a simplified model it is illustrated that the residual interaction used in a ring approximation must fulfill some restrictions in order to qualitatively reproduce the full RPA results.

nucl-th↗

arXiv1998

Analysis of exchange terms in a projected ERPA Theory applied to the quasi-elastic (e,e') reaction

A systematic study of the influence of exchange terms in the longitudinal and transverse nuclear response to quasi-elastic (e,e') reactions is presented. The study is performed within the framework of the extended random phase approximation (ERPA), which in conjuction with a projection method permits a separation of various contributions tied to different physical processes. The calculations are performed in nuclear matter up to second order in the residual interaction for which we take a (pi+rho)-model with the addition of the Landau-Migdal g'-parameter. Exchange terms are found to be important only for the RPA-type contributions around the quasielastic peak.

nucl-th↗

arXiv1998

On the role of the $Δ(1232)$ on the transverse nuclear response in the $(e,e')$ reaction

The transverse nuclear response to an electromagnetic probe which is limited to create (or destroyed) a particle-hole ($ph$) or delta-hole ($Δh$) pair is analyzed. Correlations of the random phase approximation (RPA) type and self energy insertions are considered. For RPA correlations we have developed a scheme which includes explicitly the $Δ$ and the exchange terms. Self energy insertions over $ph$ and $Δh$ bubbles are studied. Several residual interactions based on a contact plus a ($π+ ρ$)-meson exchange potential are used. All calculations are performed in non-relativistic nuclear matter. The main effect of the $Δ$ is to reduce the intensity over the nuclear quasi-elastic peak. Exchange RPA terms are very important, while the self energy depends strongly on the residual interaction employed. We compare our final result with data for $^{40}Ca$ at momentum transfer $q=410$ and $q=550$ MeV/c.

nucl-th↗